Common Names

Kahikatea mealybug

Synonyms

Trionymus podocarpi Brittin, 1938

Biostatus and Distribution

The endemic Kahikatea mealybug was named in 1938 from females found on White pine/Kahikatea, Dacrycarpus dacrydioides and was later found on Rimu, Dacrydium cupressinum, both plant species are in Podocarpaceae. It is found in the North and South Islands in native habitats and on trees in parks.

Conservation status: This native mealybug is found trees throughout in native ecosystems and parks.

Life Stages and Annual Cycle

The Kahikatea mealybug breeds all year. There do not appear to be discrete generations. It is not known how long it takes from egg to adult. All stages live amongst the leaves of its host plants.

The adult female is oval, about 2 mm long and 1 mm wide. It is yellow-brown with two long broad dark areas on its dorsum (top). There are tiny white wax specks on the dorsum that eventually cover the whole body with white wax. There is a terminal pair of white wax filaments. The mature female has a pair of short antennae and three pairs of legs. There is no distinct division between the head or thorax (middle section of the body) and abdomen. On the underside of the body there is a short rostrum that guides the feeding stylets. After mating and when it is fully grown, the female mealybug settles on a young shoot and produces a white fluffy wax chamber at the rear end of its body. It lays orange coloured eggs into the egg sac. As it fills up, the female mealybug moves forward making the sac bigger as it continues to lay more eggs.

Nymphs hatch from the eggs and leave the egg sac. The nymphs are like small orange-brown adult females. There are three female nymphal instars (stages) and two male nymphal instars. These feeding stages grow by moulting (changing skin). The second instar male makes a fluffy white cocoon in which develop two pre-adult non-feeding stages, a prepupa and a pupa. The prepupa and pupa have wing buds. The adult male emerges from the pupa. The moulted prepupal and pupal skins are pushed out the end of the cocoon. The adult male does not have a rostrum or stylets and does not feed. When it is ready to emerge from the cocoon, the back end of the cocoon is pushed open and the male backs out. After it has opened the back of the cocoon, its wings (1 pair) expand and harden. It also grows a pair of long wax tails. It is presumed that the wax tails help balance the insect in flight. The male may mate with females of the same colony or fly to another colony to mate.

Feeding and honeydew.Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs excrete the excess sugary liquid, which is called honeydew, through a short white wax anal tube.

Walking, flying and dispersal.The adult male has legs and wings. It can walk around the stems where its cocoon was and it can fly to other stems or to different trees. Adult females and nymphs also have legs and can walk. They may move about the group of stems where they were born. In other insects with a none flying adult female, the first stage larvae or nymphs are able to disperse to new trees. They usually do this using the wind. It is likely that some first instar nymphs climb to a prominent place on a leaf or branch and await a gust of wind.

Recognition

The Kahikatea mealybug is the only mealybug found on Kahikatea, Dacrycarpus dacrydioides and Rimu, Dacrydium cupressinum (Podocarpaceae). It is most easily recognised by the presence of the long white egg sacs on young stems. The mass of white male cocoons can also alert a person to the presence of the mealybugs.

The juveniles of another scale insect, the Pyriform scale, Symeria pyriformis (Maskell, 1879) (Diaspididae) may produce a lot of flocculent wax that may superficially look like the mealybug cocoons.

Natural Enemies

No pathogens or parasitoids of the Kahikatea mealybug, Paraferrisia podocarpi, are known.

PredatorsSeveral predators have been observed feeding on the mealybugs or have been reared from their egg sacs.

A tiny wasp (Hymenoptera) is a predator of the Kahikatea mealybug, feeding on the eggs. The female wasp lays an egg in the mealybug egg sac. After hatching the larva feeds on the eggs. When the wasp larva is fully grown it pupates in the egg sac.

The larva of a predatory fly (Cecidomyiidae) also feed on the mealybug eggs. It also pupates in the egg sac. When the adult is ready to emerge, the pupa pushes through the wall of the egg sac. After the adult fly has emerged, the pupal case is left attached to the mealybug egg sac.

Many Mealybug ladybird larvae were seen on a tree and observed eating the mealybugs. It is likely that a hoverfly (Syrphidae) and a lacewing (Neuroptera) are also predators of the Kahikatea mealybug, but have not been observed feeding on the mealybug.

Host Plants

The Kahikatea mealybug is the only mealybug found on Kahikatea, Dacrycarpus dacrydioides and Rimu, Dacrydium cupressinum (Podocarpaceae). Its presence is most easily recognised by the presence of the long white egg sacs on young stems.

Feeding and honeydew.Mealybug adult females and nymphs have sucking mouthparts. Specially shaped rods called stylets are held in the short sheath-like rostrum. When it wishes to feed, the mealybug moves the tip of the rostrum onto the surface of the plant leaf or stem. The stylets are then gradually pushed into the plant and manoeuvred into the phloem (nutrient transport vessels) of the plant. The mealybugs suck the plant’s sap, which is high in sugars and low in other nutrients. Mealybugs excrete the excess sugary liquid, which is called honeydew, through a short white wax anal tube.

Additional Information

Why is there so much white wax?Most mealybugs produce much white flocculent wax with which they are covered and which also covers the areas of plants they inhabit. To the human eye this makes it much easier to find the colonies of mealybugs. However, does it make it easier for predators and parasitoids to find them, or is the white wax some kind of deterrent and warning colouration? Other insects with a scale stage also cover themselves with white wax. This suggests to me that it may be some kind of deterrent and warning.

Research ProjectIs there more than one species of Paraferrisia? The only known species, Paraferrisia podocarpi occurs only in New Zealand, on two endemic host plants that are in different genera of Podocarpaceae. Both genera, Dacrycarpus and Dacrydium have about 9 and 22 species respectively. It has been suggested that the mealybugs on Dacrycarpus dacrydioides and Dacrydium cupressinum may be two distinct species. With regards the genus of mealybug being in other countries, it is worth noting that the two genera of trees are present in New Caledonia, a counrty with which New Zealand has strong biogeographic links.

Williams DJ, De Boer JA. 1973. The taxonomy of some New Zealand Pseudococcidae (Homoptera: Coccoidea). Transactions of the Royal Entomological Society of London. 125(2): 227-252. (Created genus Paraferrisia).

Acknowledgements

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.